Abstract: If the confined aquifer is not completely cut off by the diaphragm wall during the pressure-relief process which is used for preventing the heave failure of deep excavation, the sphere of influence of ground settlement caused by pressure-relief of confined aquifer is much larger than that caused by the excavation. Therefore, the deformation characteristics of the existing shield tunnels caused by pressure-relief of confined aquifer are simulated by finite element method; and then the diaphragm wall is inserted into the confined aquifer, the effect of the length of diaphragm wall into the confined aquifer on the deformation of tunnel is analyzed. The results show that, as the length of diaphragm wall inserted into the confined aquifer increases, the settlement of tunnel decreases. But because of the deformation of wall, horizontal movement of the tunnel is considerable during the pressure-relief process. So it should be pointed out that when the tunnel is close to the dewatering well, even there is a diaphragm wall cutting off the confined aquifer, the influence of dewatering on the horizontal deformation should be paid attention to. Besides, the long-term pressure-relief process will cause severe settlement of the tunnel; so it should be avoided when the confined aquifer is not completely cut off.

Key words: confined aquifer, diaphragm wall, existing tunnel, pressure-relief of confined aquifer for dewatering